Electrical-line tapper



July 15, 1958 1. s. BLONDER ELECTRICAL-LINE TAPPER Filed April 8. 1955 3 SheetsSheet l m T m ISAAC S. BLO/VOER ATTORNEYS July 15, 1958 1. s. BLONDER ELECTRICAL-LINE TAPPER 5 Sheeis-Sheet 2 Filed April 8, 1955 A TTORNE VS R R m mmvm we maw M W B ANTENNA July 15, 1958 Filed April 8. 1955 l. s. BLONDER 2,843,827

ELECTRICAL-LINE TAPPER 5 Sheets-Sheet 3 IN VENTOR.

ISAAC S. BLO/VDER ATTORNEYS United States Patent The present invention relates to electrical-line tappers and, more particularly, to coaxial-line tappers of the type utilizing a conductive clamping block that is secured to the coaxial transmission line at any desired tap-off point.

The art has struggled for many years with the necessity for providing a rugged and properly performing coaxial-line electrical rapper. The problems attendant upon such devices are numerous. Many of the prior-art proposals for example, have solved the problem of providing a non-slipping tap from the coaxial line, but these priorart proposals have been subject to other disadvantages including mechanical complexity, electrical contact irregularities due to moisture and other causes, and the presenting of impedance discontinuities and inadequate signal isolation at the tap-off point. An antenna distribution system or an amplifier system may, for example, feed radio-frequency signals along a main out-door coaxial transmission line from which it is desired to tap oif thesignals at a plurality of predetermined points for such purposes as, for example, the distribution of the signals to a plurality of radio or television receivers. Under such circumstances, the problems of maintaining continuous electrical contact irrespective of the effects of moisture or weather and of providing adequate signal isolation between the line and the various tap-otf points is extremely important. It is desirable, moreover, that this isolation be accomplished without the necessity for external filters or similar apparatus additional to the tapoff structure itself.

An object of the present invention, therefore, is to provide a new and improved electrical tapper that is not subject to the above-mentioned disadvantages and that, on the contrary, not only provides excellent electrical and mechanical connection to a main electrical line, but, in addition, provides inherent signal isolation at the tap-ofli point.

An additional object is to provide such a tapper that is particularly adapted for use with coaxial transmission lines and that, in addition, is easy to manufacture and to assemble and disassemble.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawings,

Fig. 1 of which is an exploded perspective view, partly in section, illustrating the details of construction of a preferred embodiment of the present invention;

Fig. 2 is a similar view illustrating the commencement of the assembling of the parts of the apparatus of Fig. 1

Fig. 3 is a perspective view of the assembled apparatus of Fig. 1;

Fig. 4 is a view of a step preparatory to the application of the tapper of Fig. 3 to the coaxial line;

Fig. 5 is a view of the final clamping of the tapper to the coaxial line;

Fig. 6 is a similar view of the invention as applied to a wall outlet;

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Fig. 7 is a side elevation, partly sectionalized, illustrating the relative positions of the assembled parts of the tapper; and

Fig. 8 is a schematic circuit diagram of an electrical circuit equivalent to the apparatus of Figs. 1 and 7.

Referring to Fig. l, the tapper of the present invention is of the type embodying a conductive cylindrical clamping block 1 having at its upper end a transverse partially cylindrical recess 3 for receiving an insulation-covered coaxial line. Such coaxial lines customarily have outer insulation, as shown at 5, an outer sheath conductor 7 surrounding an inner insulation region 9, and an inner conductor ll disposed within the insulation 9. Within the recess 3, at opposite ends thereof, the clamping block 1 is provided with one or more conductive prods 13 extending-into the recess for puncturing or piercing the outer insulation 5 of the coaxial line and making contact with the outer sheath conductor 7. The cylindrical block I. is provided with an internally threaded intermediate aperture 15 preferably disposed along its longitudinal axis and intersecting the recess 3 at the opening 17. The lower end of the block 1, as shown in Fig. l, is exteriorly threaded at 19 for a purpose later explained.

An insulating tubular cylindrical member 21, threaded at itslower portion 23, carries at its upper end a conductive terminal prod 25 of length greater than the length of the prod or prods 13. The terminal prod 25 is preferably mounted in place at the upper end of the insulating tubular member 21 by means of an eyelet 29 having an internal flange 31. The eyelet 29 and prod 25 may be made integral, if desired, and. may be riveted over the inner surface of the upper aperture of the member 21, as at 31. At the other end of the member 21 there is provided a transverse slot 33 for permitting the insertion of a screw-driver or other tool 27, Fig. 2, in order to thread the member 21 into the upper portion of the threads of the aperture 15 ofthe clamping block 1. When so threaded, the terminal prod 25 extends longitudinally into the recess 3 through the opening 17. The opening 17 need only be of sufiicient cross section to compensate for manufacturing tolerances in the threads 23 and 15 so that there is no danger of the prod 25 contacting the walls of the opening 17, which would cause a short-circuit. Further to guard against such short-circuiting, the sides of the prod 25 below the terminal point thereof may be covered with insulation, such as an enamel coating. As shown in the drawings, the length of the tubular member 21 is less than the length of the aperture 15 so that there is unoccupied space in the lower part of the aperture 15 after the member21 is threaded therein. With the member 21 carrying the terminal prod 25 thus seated in the aperture 15 of the clamping block 1, an electrical resistor, preferably of tubular form, as shown at 25', is inserted within the tubular member 21. e The resistor 25 has a pair of longitudinally extending terminal conductors 35 and 37. Disposed about the terminal conductor 37 is an insulating dielectric tubular covering 39 as of ceramic material. The ceramic tube 39 may be secured to the terminal conductor 37 in any desired manner. It is preferred that the securing take place by silver-firing the inner wall of the ceramic tube 39 and then soldering the fired wall at 41 to, and preferably along the complete length of, the terminal conductor 37. A conductive cylindrical tubular member 43, such as an eyelet having an external flange 45, is secured, as, for example, by the same silver-firing and soldering technique, to the outer wall of the tubular insulating covering 39, in capacitive relation with the terminal conductor 37. This contruction of the capacitance 37, 39, 43, provides a large area of solder connection and is mechanically far superior to a mere side-by-side solder connection of conventional resistor and capacitance terminal conductors, which would otherwise be necessary. Through this construction, furthermore, the insulating tubing 21 completely weatherproofs the resistor 25 and the capacitance 37, 39, 43, so that even if moisture entered the line tapper channel 3 it could not affect the connections of these elements. As later explained, moisture cannot impair the prod-toinner conductor sealed contact 73, either.

The flange 45 is always clear of the tubular member 21 when the assembly 2543 is inserted within the tubular member 21 through suflicient dimensioning of the resistor 25 and its upper terminal conductor 35. It has been found preferable to provide a clearance of about A of an inch to insure satisfactory mechanical and electrical contact between the conductor 35 and the prod 25. Against the lower surface of the flange 45 there is engaged the right-hand or upper end of a preferably helical spring 47 of slightly greater diameter or crosssection than the cross-section of the conductive member 43. Into the other end of the helical spring 47 is inserted the inner conductor plug 49 of a male coaxial-line connector 51, the outer conductor sleeve 53 of which is shown interiorly threaded at 55. The coaxial-line con nector 51 will be recognized as of the conventional present-day widely used type in which the plug 49 is mounted by a flange 57 upon an insulator 59 that separates it from an outer conductor 61 of the connector which, in turn, is engaged by the conductive sleeve 53. A further coaxial line '79'-11', such as a tap-off or distribution line section, is connected between the outer conductor 61 and the plug 49 by soldering or otherwise securing the outer sheath conductor 7 of this further coaxial line, Fig. 7, to an extension 63 of the outer conductor 61 of the coaxial connector 51 and by inserting the inner conductor 11' of the further coaxial line within an opening 65 to make contact at point 64 with the plug 49. The internal threads 55 within the outer conductor sleeve 53 of the coaxial-line connector 51 and the before-mentioned external threads 19 at the lower end of the clamping block 1 are cut to cooperate with one another so that the sleeve 53 may be threaded over the threads 19 to draw the complete assembly to-. gether. This threading operation may be effected with the aid of a knurled surface 67 customarily placed upon the sleeve 53 of the coaxial-line connector 51, as more particularly shown in Fig. 3. When so drawn together, the outer conductor ill-53 of the coaxial-line connector 51 is then in excellent electrical and mechanical contact with the conducting block 1 and the spring 47 is placed under compression between the flange 57 of the plug 49 of the coaxial-line connector 51 and the under surface of the flange 45 of the conductive member 43.

The main coaxial line to which the line tapper of the present invention is to be applied may then be prepared for the application of the tapper. This is preferably done with the aid of a punch 69 that may be carried at the other end of the tool 27. This punch 69, if desired, may be slotted to improve its cutting operation and it may be used to pierce the outer insulation 5 of the main coaxial line 5-79-11 to cut not only through the outer insulation 5, but, also, through the outer sheath conductor 7. The opening thus cut through the outer insulation 5 and the outer sheath conductor 7 is clearly illustrated at '71 in Fig. 7. it is important, for the purposes of the present invention, as contrasted with prior-art connectors, that the opening 71 does not extend through the inner insulation 9 to expose the inner conductor 11. The opening 71 should be considerably larger than the cross dimension of the prod 25 in order to prevent possible contact between the prod and the edges of the outer conductor sheath 7 surrounding the opening 71. The prod 25 may then easily be inserted into the opening 71 Without fear of cont-acting and thus short-circuiting to the outer coaxial-line conductor 7, and it may pierce the insulation 9 in order to make engagement at the point 73, Fig. 7, with the inner coaxial-line conductor 11. Since the opening '71 does not extend through to the inner conductor 11, the connection 73 between the prod 25 and the inner conductor 11 is completely weather and moisture sealed, and, unlike in prior connectors, cannot become contaminated, corroded, or intermittent. Since the prod 25 pierces its own way through the insulation 9 to the inner conductor 11, moreover, the alinement of the opening 71 with the axis of the clamp 1 is not critical and the opening 71 can be formed at any desired time, even before the tapper 1 is available.

By rotating the prod 25 to advance it into contact with the inner conductor 11, through the use of the threads 23, the pointed end of the prod 25 bites into the conductor 11, providing negligible contact resistance. Were the prod 25 merely to be pressed against an exposed inner conductor 11, as in prior-art devices, the copper oxide or other contaminating layers upon the surface of the inner conductor 11 would provide an unreliable and often high-resistance contact.

An upper clamping member or lid 2, Figs. 1, 4 and 5, may then be secured over the coaxial line to the clamping block 1 by means of bolts 4 received within apertures 6 in the cap 2. and corresponding apertures 8 in the upper surface of the conducting block 1.

The construction above described not only provides for a rigid connection of the line tapper of the present invention to the main coaxial line 5-7-9-11, but it inherently provides a signal isolation impedance and a direct-current isolation impedance for the tap-off line 57'--9- 11. This may be more easily understood by considering the equivalent circuit of the apparatus of Fig. 7, as illustrated in Fig. 8. The resistance of the resistor 25' is conventionally illustrated at 25' in Fig. 8. The capacitance provided between the conductive tubular member or eyelet 43 and the lower terminal conductor 37 of the resistor 25, with the dielectric medium 39 therebetween, is connected in series with the resistance 25 and inner conductor 11' of the tapoff coaxial line 7--11'. The resistor 25 provides the desired signal isolation for the tap-off. The capacitance provided by the members 37, 39, 43 is, as before stated, automatically series-connected with this signal-isolation resistance and provides direct-current isolation for the tapped-off signal. As a typical illustration, in the case of a 75-ohm conventional coaxial line employed for carrying television signals, the resistor 25' may have a value of about 470 ohms, or more, in order to provide a sufiicient degree of signal isolation. With the ceramic tube 39 and eyelet 43 before mentioned, mounted upon a short length of terminal conductor 37 about threeeights of an inch, a capacitance of the order of about 15 microfarads may be provided which has been found to provide satisfactory direct-current isolation in the tapoff line.

While the tapper of the present invention has been described as cooperating with a male coaxial-line connector 51, it is to be understood that it may also be utilized with any other desired type of line connector, as well as with other types of transmission lines. In Fig. 6, for example, the tapper 1 is secured within a recess 76 in a wall 77 of a room, as by screws 83 and a lock nut 79, to an outlet plate bracket 78 to which is also connected, as at 81, a coaxial-line outlet 69. The outlet 69 protrudes through a wall outlet plate 72 secured to the upper and lower offset portions of the bracket 78 by screws 75 to cover the wall recess 76. A tap-off coaxial line 5', similar to the line 5, 7, 9', 11' of Fig. 7, may be conveniently connected within the room to the outlet 69 in order to feed signals from, for example, the main antenna line 5 to a receiver.

Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a coaxial-line electrical: tapper of the ,type having a conductive clamping clock provided with one, or more prods for piercing the outer insulation ofthe line in order to contact the outer conductor thereof while clamping the line and a pointed terminal prod insulated from, the block for piercing the insulation between the inner and outer conductors of the line in order to establish electrical connection with the inner conductor, the combination of a series-connected resistor and capacitor, a coaxial-line connector having an outer conductor and winner conductor, a helical spring disposed between the said coaxial-line inner conductor and the capacitor, and means for electrically and mechanically securing the coaxial-line-connector outer conductor to the clamping block while placing the spring under compression to urge theseries-connected resistor and capacitor into series connection with the said terminal prod.

2. In a coaxial-line electrical tapper of the type having a conductive clamping block provided with. oneror more prodsfor piercing the outer insulation of the line in order to contact the outer conductor thereof while clamping the line and a pointed terminal prod insulated fromthe block and provided with means for threadedly advancing the prod to pierce the insulation between the inner and outer conductors of the line in order to establish electrical connection with the inner conductor, the combination of a series-connected resistor and capacitor, a male coaxialline connector having an outer conductor and an innerconductor plug, a helical spring disposed between the plug and the capacitor, and means for electrically and mechanically securing the coaxial-line-connector outer conductor to the clamping block while placing the spring under compression to urge the series-connected resistor and capacitor into series connection with the said terminal prod.

3. A coaxial-line electrical tapper having, in combination,a conductive clamping block provided with one or more prods and having an aperture containing a pointed terminal prod insulated from the block and-threadedly movable with respect to the block, a series connected resistor and capacitor, a male coaxial-line connector having an outer conductor and an inner-conductor plug, a helical spring disposed between the plug andthe capacitor, and means for electrically and mechanically securing the coaxial-line-connector outer conductor to the clamping block while placing the spring under compression to urge the series-connected resistor and capacitor into series connection with the said terminal prod.

4. In a coaxial-line electrical tapper of the'type having a conductive clamping block provided with one or more prods for piercing the outer insulation of the line in order to contact the outer conductor thereof While clamping the line and a terminal prod insulated from the block for piercing the insulation between the inner and outer conductors of the line in order to establish electrical connection with the inner conductor, the combination of a resistor having a pair of longitudinally extending terminal conductors one of which engages the said terminal prod, an insulating covering for the other terminal conductor, a conductive tube disposed about the insulating covering and having a flange disposed at its end nearer the resistor, a male coaxial-line connector having an outer conductor and an inner-conductor plug provided with a flange at its inner end, a helical spring of cross" section larger than that of the said plug and the'said tube for receiving the same at opposite ends, and means for electrically and mechanically securing the coaxial-line-connector outer conductor to the clamping block While placing the spring under compression between the said flanges of the said plug and the said tube.

5. In a coaxial-line electrical tapper of the typejhaving a conductive clamping block provided with one or more prods for piercing the outer insulationof the line inorder to contact the outer conductor thereof while clamping the line and a terminal prod insulated from the block for piercing theinsulation between the inner and outer conductors of the line in order to establish electrical connection with the inner conductor, the combination of a resistor having a pair of longitudinally extending terminal conductors one of which engages the said terminal prod, an insulating covering for the other terminal conductor, a conductive tube disposed about the insulating covering and having a flange disposed at its end nearer the resistor, a coaxial-line connector having an outer conductor and an inner conductor, a helical spring of cross section larger than that of the inner conductor and the said tube for receiving the same at opposite ends, and means for electrically andmechanically securing'the coaXial-line-connector outer conductor to the clamping block While placing the spring under compression between the said flange of the said tube and the said inner conductor of the coaxial-line connector.

6. A coaxial-line electrical tapper having, in combination, a conductive clamping block provided with one or more prods and having an aperture containing a terminal prod insulated from the block, a resistor having a pair of longitudinally extending terminal conductors one of which engages the said terminal prod, an insulating covering for the other terminal conductor, a conductive tube disposed about the insulating covering and having a flange disposed at its end nearer the resistor, a male coaxial-line connector'having an outer conductor and an inner conduct-or plug provided with a'flange at its inner end, a helical spring of cross section larger than that of the said plug and the said tube for receiving the same at opposite ends, and means for electrically and mechanically securing thecoaxial-line-connector outer conductor to the clamping block while placing the spring under compression between the said flanges of the said plug and the said tube.

7. A coaxial-line electrical tapper having, in combination, a conductive clamping block having at one end a transverse recess provided with one or more prods projecting longitudinally into the recess and threaded at its other end, the block having an aperture intermediate the recess containing a terminal prod insulated from the block, a resistor disposed within the said aperture having a pair of longitudinally extending terminal conductors one of which engages the said terminal prod, an insulating covering for the other terminal conductor, a. conductive tube disposed about the insulating covering and having a flange disposed at its end nearer the resistor, a male coaxial-line connector having a threaded outer conductor and an inner-conductor plug provided with a flange at its inner end, and a helical spring of cross section larger than that of the said plug and the said tube for receiving the same at opposite ends, the said threaded other end of the clamping block being secured in threaded engagement with the said threaded outer conductor of the coaxial connector with the spring under compression between the said flanges of the said plug and the said tube.

8. A coaxial-line electrical tapper having, in combination, a conductive clamping block having at one end a transverse recess provided with one or more prods projecting longitudinally into the recess and threaded at its other end,v the block having a longitudinally extending threaded intermediate aperture, an insulating tubular member of length less than the length of the aperture threaded within the end of the aperture adjacent the said recess and terminating at one of its ends in a terminal prod extending longitudinally into the said recess, a resistor having, a pair of longitudinally extending terminal conductors and disposed within the said insulating tubular member with one of the terminal conductors engaging the and having a flange disposed at its end nearer the resistor seating against the other end of the insulating tubular member, a male coaxial-line connector having a threaded outer conductor and an inner-conductor plug provided with a flange at its inner end, and a helical spring of cross section larger than that of the said plug and the said conductive tube for receiving the same at opposite ends, the said threaded other end of the clamping block being secured in threaded engagement with the said threaded outer conductor of the coaxial connector with the spring under compression between the said flanges of the said plug and the said conductive tube.

9. A coaxial-line electrical tapper having, in combination, a cylindrical conductive clamping block having at one end a transverse recess provided with one or more prods projecting longitudinally into the recess and threaded at its other end, the block having a longitudinally extending threaded intermediate aperture, an insulating tubular member of length less than the length of the aperture threaded within the end of the aperture adjacent the said recess and terminating at one of its ends in a conductive eyelet carrying a terminal prod extending longitudinally into the said recess, a resistor having a pair of longitudinally extending terminal conductors and disposed within the said insulating tubular member with the position of the resistor limited by the said eyelet and with one of the terminal conductors engaging the said terminal prod and the other terminal conductor extending outside the insulating tubular member, an insulating covering for the said other terminal conductor, a conductive tube disposed about the insulating covering and having a flange disposed at its end nearer the resistor seating against the other end of the insulating tubular member, a male coaxial-line connector having a threaded t outer conductor and an inner-conductor plug provided with a flange at its inner end, and a helical spring of cross section larger than that of the said plug and the said conductive tube for receiving the same at opposite ends, the said threaded other end of the clamping block being secured in threaded engagement with the said threaded outer conductor of the coaxial connector with the spring under compression between the said flanges of the said plug and the said conductive table.

10. A coaxial-line electrical tapper having, in combination, a conductive clamping block having at one end a transverse recess provided with one or more prods projecting longitudinally into the recess and threaded at its other end, the block having a longitudinally extending threaded intermediate aperture, an insulating tubular member of length less than the length of the aperture 7 threaded within the end of the aperture adjacent the said recess and terminating at one of its ends in a terminal prod extending longitudinally into the said recess, a resistor having a pair of longitudinally extending terminal conductors and disposed within the said insulating tubular the insulating tubular member, a male coaxial-line con- Y nector having a threaded outer conductor and an innerconductor plug provided with a flange at its inner end, and a helical spring of cross section larger than that of the said plug and the said conductive tube for receiving the same at opposite ends, the said threaded other end i of the clamping block being secured in threaded engagement with the said threaded outer conductor of the coaxial connector with the spring under compression between the said flanges of the said plug and the said conductive tube.

11. A coaxial-line electrical tapper as claimed in claim 8 and in which the said insulating tubular member is provided at its said other end with a transverse slot for permitting the insertion of a screw driver and the like to seat the said member Within the said clamping-block aperture.

12. In a coaxial-line electrical tapper of the type having a conductive clamping block provided with one or more prods for piercing the outer insulation of the line in order to contact the outer conductor thereof while clamping the line and a terminal prod insulated from the block for piercing the insulation between the inner and outer conductors of the line in order to establish electrical connection with the inner conductor, the combination of a resistor having a pair of longitudinally extending terminal conductors one of which engages the said terminal prod, an insulator for the other terminal conductor, a conductivemember disposed adjacent the insulator and having a flange, a male coaxial-line connector having an outer conductor and an inner-conductor plug, a helical spring of cross section larger than that of the said plug and the said conductive member for receiving the same at opposite ends, and means for electrically and mechanically securing the coaxial-'line-connector outer conductor to the clamping block while placing the spring under compression between the said flange of the said conductive member and the said plug.

13. A coaxial-line electrical tapper having, in combination, a conductive clamping block having at one end a transverse recess provided with one or more prods projecting longitudinally into the recess and threaded at its other end, the block having a longitudinally extending intermediate aperture, an insulating tubular member of length less than the length of the aperture disposed Within the end of the aperture adjacent the said recess and terminating at one of its ends in a terminal prod extending longitudinally into the said recess, a resistor having a pair of longitudinally extending terminal conductors and disposed within the said insulating tubular member with one of the terminal conductors engaging the said terminal prod, a ceramic insulating tubular covering for the other terminal conductor of the resistor, a conductive tube disposed about the insulating covering and having a flange, a male coaxial-line connector having a threaded outer conductor and an inner-conductor plug provided with a flange at its inner end, and a helical spring of cross section larger than that of the said plug and the said conductive tube for receiving the same at opposite ends, the said threaded other end of the clamping block being secured in threaded engagement with the said threaded outer conductor of the coaxial connector with the spring under compression between the said flange of the said conductive tube and the said flange of the plug.

14. A coaxial-line electrical tapper having, in combination, a conductive clamping block provided with one or more prods and having an aperture containing a pointed terminal prod insulated from the block, isolating impedance means comprising a series-connected resistor and capacitor, a coaxialline connector having an outer conductor and an inner conductor, resilient means disposed between the said coaxial-line inner conductor and the isolating impedance means, and means for electrically and mechanically securing the coaxial-line-connector outer conductor to the clamping block while placing the resilient means under compression to urge the series-connected resistor and capacitor into series connection with the said terminal prod.

References Cited in the file of this patent UNITED STATES PATENTS 

